Currently, one-dimensional nanostructured binary metal oxides attract a great attention in supercapacitors (SCs) application due to their rapid charge transportation. In this respect, different nanostructures of FeCo₂O₄ are designed by simply tuning the reaction temperature in hydrothermal synthesis. These nanostructures are directly grown on flexible stainless steel mesh and further applied as binder-free electrodes for SCs. The systematic study is carried out to confirm the relation between surface characteristics and electrochemical properties of FeCo₂O₄ thin film. Among different nanostructures, FeCo₂O₄ nanowire arrays exhibit hierarchical mesoporous structure and demonstrate good surface properties including high surface area and appropriate pore volume. As a consequence, relatively high specific capacitance of 1963 F g⁻¹ is obtained for the FeCo₂O₄ nanowire electrode. Further, asymmetric SC is fabricated using nanowired-FeCo₂O₄ and nanoparticulated-MnO₂ thin films as negative and positive electrodes with neutral Na₂SO₄ electrolyte. Impressively, the MnO₂//FeCo₂O₄ cell could be successfully cycled in a wide voltage window of 2.0 V, which can achieve a specific capacitance of 218 F g⁻¹ and energy density of 43 Wh kg⁻¹. In addition, the SCs exhibit improved capacitance with cycling, which is attributed to opening of micro-pores occurred by frequent ion transport.

Flow batteries are one option for future, low-cost stationary energy storage. We present a perspective overview of the potential cost of organic active materials for aqueous flow batteries based on a comprehensive mathematical model. The battery capital costs for 38 different organic active materials, as well as the state-of-the-art vanadium system are elucidated. We reveal that only a small number of organic molecules would result in costs close to the vanadium reference system. We identify the most promising candidate as the phenazine 3,3′-(phenazine-1,6-diylbis(azanediyl))dipropionic acid) [1,6-DPAP], suggesting costs even below that of the vanadium reference. Additional cost-saving potential can be expected by mass production of these active materials; major benefits lie in the reduced electrolyte costs as well as power costs, although plant maintenance is a major challenge when applying organic materials. Moreover, this work is designed to be expandable. The developed calculation tool (ReFlowLab) accompanying this publication is open for updates with new data.